In his introduction to The Annotated Huckleberry Finn, Michael Patrick Hearn writes that Twain "could be uninhibitedly vulgar", and quotes critic William Dean Howells, a Twain contemporary, who wrote that the author's "humor was not for most women". However, Hearn continues by explaining that "the reticent Howells found nothing in the proofs of Huckleberry Finn so offensive that it needed to be struck out".
Much of modern scholarship of Huckleberry Finn has focused on its treatment of race. Many Twain scholars have argued that the book, by humanizing Jim and exposing the fallacies of the racist assumptions of slavery, is an attack on racism. Others have argued that the book falls short on this score, especially in its depiction of Jim. According to Professor Stephen Railton of the University of Virginia, Twain was unable to fully rise above the stereotypes of black people that white readers of his era expected and enjoyed, and, therefore, resorted to minstrel show-style comedy to provide humor at Jim's expense, and ended up confirming rather than challenging late-19th century racist stereotypes.
In one instance, the controversy caused a drastically altered interpretation of the text: in 1955, CBS tried to avoid controversial material in a televised version of the book, by deleting all mention of slavery and omitting the character of Jim entirely.
Because of this controversy over whether Huckleberry Finn is racist or anti-racist, and because the word "nigger" is frequently used in the novel (a commonly used word in Twain's time which has since become vulgar and taboo), many have questioned the appropriateness of teaching the book in the U.S. public school system—this questioning of the word "nigger" is illustrated by a school administrator of Virginia in 1982 calling the novel the "most grotesque example of racism I've ever seen in my life". According to the American Library Association, Huckleberry Finn was the fifth most frequently challenged book in the United States during the 1990s.
There have been several more recent cases involving protests for the banning of the novel. In 2003, high school student Calista Phair and her grandmother, Beatrice Clark, in Renton, Washington, proposed banning the book from classroom learning in the Renton School District, though not from any public libraries, because of the word "nigger". Clark filed a request with the school district in response to the required reading of the book, asking for the novel to be removed from the English curriculum. The two curriculum committees that considered her request eventually decided to keep the novel on the 11th grade curriculum, though they suspended it until a panel had time to review the novel and set a specific teaching procedure for the novel's controversial topics.
In 2009, a Washington state high school teacher called for the removal of the novel from a school curriculum. The teacher, John Foley, called for replacing Adventures of Huckleberry Finn with a more modern novel. In an opinion column that Foley wrote in the Seattle Post Intelligencer, he states that all "novels that use the ‘N-word' repeatedly need to go." He states that teaching the novel is not only unnecessary, but difficult due to the offensive language within the novel with many students becoming uncomfortable at "just hear[ing] the N-word." He views this change as "common sense," with Obama's election into office as a sign that Americans "are ready for a change," and that by removing these books from the reading lists, they would be following this change.
Publishers of the book have made their own attempts at easing the controversy by way of less-coarse publications. A 2011 edition of the book, published by NewSouth Books, replaced the word "nigger" with "slave" (although being incorrectly addressed to a freed man) and did not use the term "Injun." Mark Twain scholar Alan Gribben said he hoped the edition would be more friendly for use in classrooms, rather than have the work banned outright from classroom reading lists due to its language.
According to publisher Suzanne La Rosa "At NewSouth, we saw the value in an edition that would help the works find new readers. If the publication sparks good debate about how language impacts learning or about the nature of censorship or the way in which racial slurs exercise their baneful influence, then our mission in publishing this new edition of Twain's works will be more emphatically fulfilled." Another scholar, Thomas Wortham, criticized the changes, saying the new edition "doesn't challenge children to ask, 'Why would a child like Huck use such reprehensible language?'"
In 2016, Adventures of Huckleberry Finn was removed from a public school district in Virginia, along with the novel To Kill a Mockingbird, due to their use of racial slurs.
Responses to this include the publishing of The Hipster Huckleberry Finn which is an edition with the word "nigger" replaced with the word "hipster". The book's description includes this statement "Thanks to editor Richard Grayson, the adventures of Huckleberry Finn are now neither offensive nor uncool."